Dry-type transformer



June 19, 1956 CAMILLI ET AL DRY-TYPE TRANSFORMER 2 Sheets-Sheet 1 Filed Dec. 15, 1951 Inventors: Guglielmo CamiHi, Friend H.Kier-stead,

ne JVandenQrift, John C. Russ, by

Way

Their Attorney.

United States Patent DRY-TYPE TRANSFORMER Guglielmo Camilli, Friend H. Kierstead, Wayne J.

Vandergrift, and John C. Russ, Pittsiield, Mass., assignors to General Electric Company, a corporation of New York Application December 13, 1951, Serial No. 261,544 Claims. (Cl. 336-60) This invention relates to stationary electrical induction apparatus, and more particularly to a new and improved construction for stationary electrical induction apparatus of the dry type.

The modes of heat transfer in dry-type (air insulated) stationary electrical induction apparatus, such as dry-type transformers, are essentially the same as those of liquidinsulated stationary electrical induction apparatus. Convection plays a most important role in both types of stationary electrical induction apparatus. In large transformers the natural convection circulation of the cooling medium is generally supplemented at higher loads by forced circulation of the cooling medium. In large oilfilled transformers, for example, cooling by convection is supplemented by circulation of the oil by means of pumps, and in air-insulated transformers, circulation of the air is obtained by means of fans or blowers. Air-insulated transformers are generally enclosed in a metal casing and the cooling air is allowed to enter and leave the casing through openings or louvers made in the metal casing.

it is an object of this invention to provide a new and improved construction for dry-type stationary electrical induction apparatus which will provide an improved cooling characteristic for such apparatus, particularly under natural draft conditions.

It is a still further object of this invention to provide a cooling arrangement for stationary electrical induction apparatus which will reduce the hot spot temperature of the windings of such apparatus.

Another object of this invention is to provide a cooling arrangement for stationary electrical induction apparatus which will tend to equalize temperature distribution axially of the windings of the apparatus.

In accordance with these objectives, this invention provides an arrangement of baflies and windings for a dry type stationary electrical induction apparatus in which bafiles and windings are so arranged as to provide an in-..

creased cooling in the region of winding hot spots.

The features of this invention which we believe to be novel are set forth in the appended claims. Our invention itself, however, both as to its organization and use, together with further objects and advantages thereof, may

best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents a dry type transformer having a baflle member in accordance with our invention; Figs.

2, 3, 4 and 5 are graphical representations of the effect of bafile placement on hot spot temperature of a dry type transformer winding; Fig. 6 is an elevation view, in

' section, of a transformer having a baffle member in accordance with our invention and a sectionalized disk type winding with separate cooling ducts for each winding section; while Fig. 7 is an embodiment of our baflle arrangement in connection with a barrel type winding.

Referring now to Fig. 1, there is shown an enclosing means or casing 1 having contained therein a magnetic core 2 upon which are mounted two low voltage barrel type windings 3 and 4, and a high voltage disk type winding 5. Barrel winding 4 is positioned radially outwardly of barrel winding 3 and is separated therefrom by an axially-extending duct 6. Disk winding 5 is positioned radially outwardly of barrel winding 4 and is separated radially therefrom by an axially-extending duct 7. The laminations comprising magnetic core 2 are held together in assembled relation by means of core clamps 8 and 9 which extend across the upper and lower ends, respectively, of the magnetic core. The casing 1 in which the stationary electrical induction apparatus is contained is provided with louver openings 10 at the upper and lower side surfaces of the casing.

The electrical windings shown in Fig. 1 are positioned about one of the legs of the magnetic core, and it will be understood that the magnetic core may be provided with one, two, or more such winding legs.

The windings and core of the stationary electrical induction apparatus may be cooled partially or entirely by the natural convection flow of air through the casing. Such a draft of cooling air is promoted partially by the use of the louvers 10 at the upper and lower side surfaces of the casing. Air drawn in through louvers at the lower part of the casing is heated during operation of the apparatus and rises to the top of the casing and escapes through the openings or louvers situated along the upper side surfaces of the casing. The warm air is constantly replaced by cool air which enters the casing through the louver openings placed on the lower side surfaces of the casing.

Fan members 11 may be positioned interiorly of the casing on opposite sides of the transformer winding and suitably mounted adjacent the lower end of the casing in such manner as to provide a circulation of air about the windings. When the transformer is equipped with fans, the fans generally operate only at higher loads on the transformer, with the transformer being cooled by natural draft at lower loads. If only one fan 11 is used on each side of the casing, it should be suitably positioned with respect to the one or more windings legs of the transformer core so as to provide a substantially equal cooling effect for the windings on each of the core legs. However, a plurality of such fans may be used on each side of the casing, in which case the plurality of fans would be positioned in such manner as to provide a substantially equal flow of cooling air to the windings of the one or more winding legs. Slots 12 should be provided in the base of the transformer casing adjacent the outer edges of the casing, in order to provide an additional air intake for the fans 11.

in accordance with our invention, in order to further promote the cooling effect, we position a baflie member 13 adjacent the upper end of the electrical windings at a height corresponding substantially to the height of the hot spot of the high voltage disk winding. The bafile member 13 extends from the inner surface of the casing 1 to adjacent the outer periphery of the winding 5. A space of the magnitude of from one-eighth to one-fourth inch is left between the outer periphery or circumference of the winding 5 and the adjacent edge of bafile member 13.

We have found by experiment that under identical loading conditions, the hottest spot and the average temperature of both the high and low voltage windings can be appreciably reduced by the use of one or more baffle members such as the baflie 13. The cooling effect in the high voltage disk winding due to the use of the bafiie member 13 can be attributed to the fact that the cooling air is constrained to pass radially inwardly across the disk winding layers just below the baffle, and radially outwardly just above the baffle, thereby producing an increased cooling.

In accordance with our invention, one or more bathe members, such as baffie member 13, may be positioned at axially displaced locations adjacent the outer periphery of the high voltage winding. Where only one baflie member is used, as shown in Fig. 1, it should preferably be located at a position corresponding substantially to the maximum natural draft hot spot temperature of the transformer winding. However, in accordance with our invention, a plurality of such bafiles may be used and axially displaced from one another adjacent the outer periphery of the high voltage winding in such manner as to cause a substantial decrease in the maximum temperature of the winding.

There is shown in Figs. 2, 3, 4 and 5, a graphical representation of the effect of the placement of barrier members in accordance with our invention on the distribution of the temperature rise over ambient of the transformer high voltage disk winding. There is shown in Fig. 2 the situation which prevails when no barrier member is used. Curve A of Fig. 2 represents the temperature rise above ambient temperature of the high voltage disk winding at various axial positions along the high voltage winding. It will be observed that curve A reaches a maximum at point 14. The location of the point 14 on outer winding '5 may be defined as the baffle-absent hottest spot and is referred to in the claims as such. The temperature rise above ambient of the high voltage winding at point 14 will be arbitrarily designated as T1. Similarly, the low voltage winding hot spot temperature rise above ambient occurs at approximately the same axial height as point 14 and will be designated as T2.

There is shown in Fig. 3 the effect of the placement of baffle 13 of Fig. 1 at an axial position corresponding to that of the hot spot temperature 14 of Fig. 2. Bafile 13 constrains the air to pass radially across the layers of the high voltage disk winding in the hot spot region with the result that the temperature at the former hot spot is greatly reduced as shown by curve B of Fig. 3, which represents the high voltage disk winding temperature rise above ambient. The placement of the baffle causes a change in the characteristic of the temperature curve of the disk winding with respect to the axial location of the disk coils so that temperature humps occur at 15 and 16 on opposite sides of the location of the baffie. In experiments which we have conducted, we have found that the temperature hump 15 has a value of .6T1 and the temperature hump 16 has a value of .7Ti. Thus, it will be seen that the introduction of a single baflle 13 reduces the maximum temperature of the disk winding from T1 to .7T1. The former hot spot of the barrel windings is reduced from T2 to .75T2 by the use of baffle 13.

It will be noted that the temperature curve B of Fig. 3 is unsymmetrical with respect to the battle l3 and that there are unequal temperature humps on either side of the bafiie, as shown at 15 and 16. In accordance with our invention, the baffle may be shifted axially along the windings as shown in Fig. 4 so that substantially equal temperature humps will be produced on either side of the battle. Thus, as is shown in Fig. 4, the baffle 13 has been shifted from its former position near the upper end of the winding closer toward the axial center of the winding, although not necessarily at the exact axial center, with the result that the temperature humps 17 and 18 of curve C each have a value of .65T1. The hot spot temperature rise of the low voltage barrel windings is still .75T2 and remains at the same axial height as point 14 of Fig. 2. This location of the bafiie in Fig. 4 which would produce temperature humps or peaks of equal magnitude in the portions of the winding disposed on axially opposed sides thereof may be defined as the equi-peak temperature position. The spot on the winding 5 which is radially opposed to this battle location may be defined as the equi-peak temperature spot.

In a further embodiment of our invention, shown in Fig. 5, more than one bafile may be used in order to still further reduce the peak values of the temperature humps and cause an approach toward an average temperature throughout the winding. Thus, as shown in Fig. 5, a plurality of battles 19, 20 and 21 may be axially positioned adjacent the outer periphery of the disk winding. Curve D of Fig. 5 shows the temperature rise above ambient of the high voltage disk winding at various axial positions when three bat-lies are used and it will be noted that wherever a baffle is positioned the temperature curve shows a decrease in temperature. Temperature humps occur at points 22, 23, 24 and 25, and the bafiies 19, iii and 21 may be so shifted along the axis of the windings that the humps 22, 23, 24, and 25 will all have substantially an equal value. For example, with the use of three bafiles, such as are shown in Fig. 5, the temperature humps may all be caused to have a value of approximately .40T1, where T1 is the maximum temperature rise of the disk winding of Fig. 2 over the ambient temperature without the use of any baflies. In this arrangement, the hot spot temperature rise of the low voltage barrel windings remains .75T2, and remains at the same axial height as point 14 of Fig. 2.

There is shown in Fig. 6 a still further modification of our invention in which in addition 'to using a bafiie member, as previously described, the high voltage winding is sectionalized and separate cooling ducts are provided for each section of the high voltage winding. Referring now to Fig. 6, there is shown a magnetic core 26 around one winding leg of which are positioned low voltage windings 27 and 23 and a high voltage disk winding designated generally as 29. For reasons which will be explained hereinafter, the high voltage 29 is sectionalized into three winding sections which have been desig nated as 30, 31, and 32, respectively. The magnetic core and windings are contained within a tank 1 provided with louver openings 10 along the side surfaces of the tank and fans 11, similar to those described in connection with the embodiment of Fig. 1.

The disk type winding 29 has been sectionalized into the three winding sections 30,31 and 32 to facilitate cooling of the disk winding 29 by the provision of separate cooling ducts for each of the winding section-s rather than having only a single duct for the entire disk winding.

As shown in Fig. 6, winding section 30 is at the upper end of the core, winding section 31 is adjacent the intermediate section of the core, and winding section 32 is positioned at the lower end of the core structure. It will be noted that a plurality of insulating cylinders 33, 34 and 35 are spaced radially outwardly of the radially outermost low voltage winding 28. Insulating cylinder 33 is spaced radially outwardly of the radially outer surface of low voltage winding 28 and extends for the entire length of the winding structure, from the upper end of winding 28 to the lower end of winding 28. The duct formed between the radially outer surface of winding 28 and the radially inner surface of insulating cylinder 33 provides a path for the flow of cooling air adjacent the radially outer surface of winding 28.

Winding section 32 of high voltage winding 29 is positioned adjacent the radially outer surface of insulating cylinder 33 and is slightly displaced radially outwardly therefrom. The displacement between the radially outer surface of cylinder 33 and the radially inner edge of disk winding section 32 provides an axial duct for the upward passage of cooling air which has passed radially inwardly across the surface of disk winding section 32. Insulating cylinder 34 is spaced radially-outwardly of the radially outer surface of insulating cylinder 33, but insulating cylinder 34 extends only for approximately the upper two-thirds of the length of the winding structure, terminating just slightly above the uppermost surface of winding section 32. The space between the radially outer surface of insulating cylinder 33 and the radially inner surface of insulating cylinder 34 thus provides a continuation of the duct for thepassage of air which has previously passed transversely and radially inwardly across the coil layers of disk winding section 32, in effect providing a chimney for the upward passage of cooling air which has been flowing across or adjacent to winding section 32. The radial thickness of the duct between the radially outer surface of cylinder 33 and the radially inner surface of cylinder 34 is substantially the same as the radial thickness of the duct between the radially outer surface of cylinder 33 and the radially inner edge of the coil layers of winding section 32 of disk winding 29.

Winding section 31 has its radially innermost edge positioned slightly displaced radially outwardly of the radially outer edge of insulating cylinder 34. Insulating cylinder 35 is positioned outwardly of insulating cylinder 34 and extends approximately one-third the overall distance from top to bottom of the winding structure and terminates slightly above the uppermost surface of winding section 31. The space between the radially outer surface of insulating cylinder 34 and the radially inner surface of insulating cylinder 35 provides a duct for the cooling air which has passed transversely across the layers of winding section 31, in effect serving as a chimney for the escape of cooling air which has passed transversely of or adjacent the surfaces of the winding section 31.

The uppermost winding section 30 has its radially innermost edge slightly displaced radially outwardly of the radially outer surface of the outermost insulating cylinder 35. The space between the radially outer surface of insulating cylinder 35 and the radially inner surface of winding section 30 provides a chimney for the passage of cooling air which passes transversely of or adjacent the surfaces of winding section 30.

By subdividing or sectionalizing the high voltage disk type winding 29 into a plurality of sections and providing a separate chimney or cooling arrangement in the form of a separate axially-extending annular cooling duct for each of the respective winding sections, as hereinbefore described, a greater cooling of the high voltage disk type winding is obtained than when the disk winding has only a single chimney or duct extending longitudinally of the entire high voltage disk winding.

A further feature, shown in Fig. 6, is the use of disk type high voltage windings which are inclined at an angle with respect to the axis of the magnetic core in such manner as to cause the disk type windings to be of frustoconical shape. The disk type winding should preferably be inclined in such a direction that the radially innermost portion of each disk winding is higher than the radially outer portion. By inclining the disk windings upwardly passage of cooling air radially inwardly across the winding surface is facilitated.

A single baffle member 36 is shown positioned adjacent the radially outer surface of disk winding 29, preferably at a height corresponding substantially to the axial height of the hot spot of the disk winding. This further facilitates the cooling of the windings, similar to the cooling obtained in connection with the embodiment of Fig. l, as shown graphically in Fig. 3.

There is shown in Fig. 7 a further embodiment of our invention as applied to a stationary electrical induction apparatus having only barrel type windings, without any disk type windings of the type shown in Figs. 1-6. There is shown in Fig. 7 a magnetic core 37 having two barrel windings 38 and 39 with barrel winding 38 being positioned radially outwardly of barrel winding 37. Fans 11 may be positioned on the floor of the enclosing tank structure adjacent the walls of the tank, with fans 11 being symmetrically positioned with respect to the winding legs of the transformer so that the windings on each of the one or more winding legs will be equally cooled by the action of the fans. A bafile member 40 is positioned adjacent the lower end of the outermost winding 39 and extends from inner periphery of the walls of the tank to closely adjacent the outer periphery of the radially outermost barrel winding 38. The baflie 40 will constrain the air circulated by the fan 11 to pass upwardly through the axial duct between the barrel windings 37 and 38 in such manner as to effectively cool these windings. By use of the baffle member 40 a much larger proportion of the air circulated by fans 11 is brought into close contact with the barrel windings 38 and 39 than would occur if the baffle 40 were not used.

It can be seen from the foregoing that we have provided a new and improved arrangement for effecting the cooling of a stationary electrical induction apparatus, such as a transformer.

It will be obvious that while we have described our invention in connection with air cooled stationary electrical induction apparatus, our invention is equally applicable for use with apparatus which is cooled by any gaseous medium.

Furthermore, while we have described and illustrated our invention in connection with a transformer, it will be obvious that our cooling arrangement is equally applicable to any type of stationary electrical induction apparatus.

While there have been shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A stationary electrical induction apparatus of the gas-insulated type comprising an enclosing casing, a mag netic core contained within said casing, said magnetic core having at least one winding leg for the reception of electrical windings, a plurality of electrical windings coaxially disposed about said winding leg, the radially outermost of said windings being a winding of the disk type, said windings being radially displaced with respect to each other and separated from each other by axially-extending ducts, said ducts providing paths for the passage of cooling gas adjacent said windings, and a baflle member extending from the inner surface of said enclosing casing to closely adjacent the radially outer surface of said disk winding in a plane substantially perpendicular to the vertical axis of said enclosing casing, said baffle member being positioned at an axial height substantially in alignment with the natural draft hottest spot of said disk winding prior to placement of said baflle.

2. A stationary electrical induction apparatus of the gas-insulated type comprising an enclosing casing, a magnetic core contained within said casing, said magnetic core having at least one winding leg for the reception of electrical windings, a plurality of electrical windings coaxially disposed about said winding leg, the radially outermost of said windings being of the disk type, said windings being radially displaced with respect to each other and separated from each other by axially extending ducts, said ducts providing paths for the passage of cooling gas adjacent said windings, and a baffie member extending from the inner surface of said enclosing casing to closely adjacent the radially outer surface of said disk winding, said bafile member being axially positioned with respect to said disk winding in such manner that substantially equal maximum temperatures are obtained in the portions of said disk winding axially disposed on opposite sides of said baflie member.

3. A stationary electrical induction apparatus of the gas-insulated type comprising an enclosing casing, a magnetic core contained within said casing, said magnetic core having at least one winding leg for the reception of electrical windings, a plurality of electrical windings coaxially disposed about said winding leg, the radially outermost of said windings being of the disk type, said windings being radially displaced with respect to each other and separated from each other by axially-extending ducts, said ducts providing paths for the passage of cooling gas adjacent said windings, and a plurality of axiallydisplaced bathe members,each of said bafile members extending from the inner surface of said enclosing casing *to closely adjacent the radially outer surface of said disk winding, "said ba'fi'le members being axially positioned in spaced relation to said disk winding to provide approximately the same maximum temperature on both sides of each cit said bafiles.

4. A stationary electrical induction apparatus of the gas-insulated type comprising an enclosing casing, a magnetic core :contained "within said casing, said magnetic core having a winding leg which has an axis about which a plurality of electrical windings are coaxially disposed, the radially outermost :of said windings being a winding of the disk type, said windings being separated from each oth'er byaxially extending ducts which provide paths for the passage of'cooling gas adjacent said windings, and a baflie member extending from the inner surface of said "enclosing casing to 'closely adjacent the radially outer surface of said disk winding, said disk Winding having a bathe-absent hottest spot which corresponds to the hottest spot of said winding prior to placement of said baffie member, said disk winding also having an equi-peak temperature spot which is radially opposed to a location at which said battle member could be positioned so as to produce equal maximum temperature rises in the portions of said disk winding axially disposed on opposite sides .of said baflile, the radially outer surface of said disk winding defining a region extending axially from said baffle-absent hottest spot to said equi-peak temperature spot but not substantially beyond these two spots, said baffle having an inner peripheral portion which throughout substantially its entire extent is positioned in axial alignment with said region.

5. A stationary electrical induction apparatus of the gas-insulated type comprising an enclosing casing, a magnetic core contained within said casing, said magnetic core having-at least one winding leg for the reception of electrical windings, a plurality of electrical windings coaxially disposed about said winding leg, the radially outer- 8 most of said windings being -a winding of the disk type, said windings being radially displaced with respect to each other and separated from each other by axially extending ducts said ducts providing paths for the passage of cooling gas adjacent said windings, and a bafile member extending from the inner surface of said enclosing casing to closely adjacent the radially outermost surface of said disk winding in a plane substantially perpendicular to the vertical axis of said enclosing casing, said disk winding comprising a plurality of superposed axially displaced winding layers, the plurality of winding layers comprising said disk winding being divided into a plurality of axially adjacent layer groups, each of said layer groups comprising a plurality :of axially adjacent winding layers, each of said layer groups being radially displaced from its axially adjacent layer groups, successive layer groups being displaced in the same radial direction, each of said respective winding layer groups having an axially extending duct adjacent the radially innermost edge of said respective winding layer group and extending to an axial endof said disk winding for conducting away from said respective winding layer group air which has passed in cooling relation to said layer group, said bafiie member being positioned at an axial height substantially in alignment with the natural draft hottest spot of said disk winding prior to placement of said bafiie.

References Cited in the file of this patent UNITED STATES PATENTS 1,183,616 Wooldridge May 16, 1916 1,304,257 Brand May 20, 1919 1,523,378 Lennox Jan. 13, 1925 1,585,448 Weed May 18, 1926 1,940,864 Hodnette Dec. 26, 1933 2,414,990 Weed Jan. 28, 1947 2,459,322 Johnston Jan. 18, 1949 FOREIGN PATENTS 213,459 Switzerland June 3, 1941 

